Recently, substantial attention has been directed to the field of superconductors and to systems and methods for using such products. Substantial attention also has been directed to systems and methods for providing a cold environment (e.g., 77.degree. K. or lower) within which superconductor products such as superconducting filter systems may function.
One device that has been widely used to produce a cold environment within which superconductor devices may function is the Stirling cycle refrigeration unit or Stirling cycle cryocooler. Such units typically comprise a displacer assembly and a compressor assembly, wherein the two assemblies are in fluid communication and are driven by one or more linear or rotary motors. Conventional displacer assemblies generally have a "cold" end and a "hot" end, the hot end being in fluid communication with the compressor assembly. Displacer assemblies generally include a displacer having a regenerator mounted therein for displacing a fluid, such as helium, from one end, i.e., the cold end of the displacer assembly, to the other end, i.e., the hot end, of the displacer assembly. The piston assembly functions to apply additional pressure to the fluid, when the fluid is located substantially within the hot end of the displacer assembly, and to relieve pressure from the fluid, when the fluid is located substantially within the cold end of the displacer assembly. In this fashion, the cold end of the displacer assembly may be maintained, for example, at 77.degree. K., while the hot end of the displacer assembly is maintained, for example, at 15.degree. K. above ambient temperature. Devices such as superconducting filter systems are then typically placed in thermal contact with the cold end of the displacer assembly.
Current Stirling cycle cryocooler designs employ a heat acceptor positioned at the cold end of the displacer assembly. The heat acceptor is typically in thermal contact with the device that is to be cooled, such as a High Temperature Superconducting Filter (HTSF) system. Heat is transferred from the device and to the heat acceptor. The heat transferred to the heat acceptor then passes to the helium gas contained in the displace assembly. The transfer of heat from the heat acceptor to the helium gas typically is the most difficult since the resistance to heat transfer is greatest in this step.
In current cryocooler designs, the ineffective transfer of heat from the heat acceptor to the helium gas results in additional power requirements. In essence, a greater amount of input power is needed to achieve the desired refrigeration lift. The lower heat transfer rate is due, in large part, to the relatively small surface area and low convective heat transfer coefficient.
There is a need for a cryocooler design that decreases the heat transfer resistance between the heat acceptor and the helium gas. The cryocooler design would advantageously require less input power to provide an equivalent amount of refrigeration as compared to prior designs.